Confocal microscopes with a diaphragm disc having many transparent regions--so-called perforated disc microscopes --are known, for example, from U.S. Pat. No. 3,926,500 and U.S. Pat. No. 4,927,254. Seen in the direction of illumination, the diaphragm disc is imaged in the focal plane of the objective on the object side, so that the object is illuminated by a pattern of points of light. The light coming from the object plane which is conjugate to the diaphragm plane is transmitted, nearly unattenuated, by the diaphragm disc, and the light coming from other object planes is strongly attenuated by the diaphragm disc. The transparent regions on the diaphragm disc are arranged so that when the diaphragm disc moves, each image point of the intermediate image coincides at a sufficiently high frequency with a transparent region. The image field is thereby scanned at a high frequency, so that a confocal image can be visually observed in the eyepiece of the microscope.
The diaphragm disc is constructed as a rotating disc in U.S. Pat. No. 3,926,500 and U.S. Pat. No. 4,927,254. The diaphragm disc must here have at least twice the diameter of the image field in the intermediate image plane, the transparent regions being arranged on a circular ring whose width corresponds at least to the image field diameter. In this so-called "modified Nipkow disc", the number of the transparent regions is therefore very large, though at any given time only about 10-15% of these transparent regions are in use. Furthermore, the diaphragm disc, due to its relatively large mass and the required high speed of rotation, must be very well balanced so that no disturbing howling occurs and no vibrations are transmitted to the microscope. Furthermore, the relatively large dimensions of the diaphragm disc make its integration into compact systems difficult.
According to U.S. Pat. No. 4,806,004, this problem was avoided by moving the diaphragm disc with the transmitting regions linearly. This can result, for example, from the transparent regions being arranged on the diaphragm disc at the corner points of a square grid and the diaphragm disc being moved at an angle which deviates from 0 degrees to 90 degrees from the grid directions, with an amplitude which varies with time in a triangular form. In this solution, the diaphragm disc needs to be only slightly larger than the diameter of the image field. Thus, more compact constructions are possible than with a rotating disc. Moreover, both the number of the transparent openings and also the mass of the disc are reduced. However, in order to prevent the transmission of the vibrations of the diaphragm disc to the microscope stand, care must be taken that the frequency of movement of the diaphragm disc does not coincide with a resonance frequency of the microscope stand.
All the solutions known heretofore have in common that the movement of the diaphragm disc always takes place along a geometrically defined, and thus deterministic, path. As a result of this even small deviations of the positions of the transparent regions on the diaphragm disc from the ideal, computed positional geometry leads to visible stripes in the image. The observer's unavoidable blinking of the eye moreover leads to a transitory visible effect which allows a scan pattern "like a flash bulb" to appear and is very irritating. For these reasons, the solutions heretofore for the visual observation of the confocal image are of only limited suitability. Moreover, with such known equipment an unpleasant visual impression arises, possibly resulting from the micro-movements of the eye together with the scanning motion of the diaphragm disc.
Furthermore, by means of intermediate tubes which are known from U.S. Pat. No. 4,884,880 and U.S. Pat. 4,884,881, the visual observation of a confocal microscopic image is possible with an already existing conventional microscope. For this purpose, U.S. Pat. No. 4,884,880 and U.S. Pat. No. 4,884,881 propose to seat an intermediate tube containing a movable diaphragm disc at the interface provided on the microscope stand for the revolving nosepiece. However, such a solution is not possible on most conventional microscopes, since the free space between the seat for the revolving nosepiece and the microscope stage is limited by the structure of the focusing drive to about 25-50 mm, so that a smaller focusing path remains with the intermediate tube installed. This holds true all the more because the beam path in the intermediate tube described there is guided in two planes which are perpendicular to the optical axis of the microscope.
Furthermore, an intermediate tube for microscopes is known from DE-A-2,428,807 (German Laid-Open Patent), and can be inserted between the eyepiece tube and the portion of the stand which carries the revolving nosepiece. This intermediate tube makes possible a rapid changeover between orthoscopic and conoscopic observation. However, the visual observation of a confocal microscope image is not possible with this intermediate tube.
Accessory devices for confocal microscopy are moreover known from U.S. Pat. No. 5,032,720 and U.S. Pat. No. 5,127,730. In them a laser beam is reflected into, and out again from, the photo tube of a conventional microscope. Apart from the fact that very high and unstable structures result from this, it is also the case with these accessory devices that direct visual observation of the confocal image via an eyepiece tube is not possible.